How to declare list of embeddable object that contains more lists inside?

Question

I have a model (object) that contains few embeddable objects inside. Few of the embeddable object have List<String> inside them. When I mark the List<Embeddable-object> @ElemenetCollection, from outside there is an issue about the string list inside.

Error : Could not determine type for: java.util.List, at table: data_room_groups, for columns: [org.hibernate.mapping.Column(images)]

Here is my entity:

private String phone;

private Star_certificate star_certificate;

@Embedded
private List<PolicyStruct> policy_struct;

private String postal_code;

@ElementCollection
private List<RoomGroup> room_groups;

@AttributeOverrides({ @AttributeOverride(name = "id", column = @Column(name = "R_ID")),
        @AttributeOverride(name = "name", column = @Column(name = "R_NAME")) })
@Embedded
private Region region;

Room Group :

private int room_group_id;

private List<String> images;

private String name;

private List<String> room_amenities;

@Embedded
private RgExt rg_ext;

private NameStruct name_struct;

Does anyone know what is the problem here? I also tried to mark the list outside as embedded and inside the list of strings as element collection , but it doesn't create the tables.